Trocars are sharp-pointed instruments used to puncture a body cavity. This is often done so that fluids may be drained using a cannula inserted into the opening. Trocars are also used during endoscopic procedures. A conventional endoscopic procedure follows three steps. The first step is the insertion of a Veress cannula into an abdominal cavity through a small incision in the abdominal wall. The cavity is inflated with insufflating gas passed through the cannula. After inflation, the Veress cannula is removed. Finally, a standard trocar housed within the bore of a trocar tube is thrust into the inflated abdomen. Standard trocars are shaped like a large metal peg with a sharpened point. The trocar is then removed and the endoscopic instrument is inserted into the abdominal cavity through the trocar tube.
Commonly owned U.S. Patents having U.S. Pat. Nos. 4,601,710 and 4,654,030 describe three embodiments of a trocar assembly having a spring-biased tubular protective shield. One of the embodiments in the former patent has a shield locking mechanism that comprises a slide valve-actuated locking tooth that engages a slot in the wall of the shield. This mechanism is cumbersome. The latter patent discloses an embodiment wherein the flap valve functions as a shield locking means by having a tip which seats against a recessed shoulder on the shield. The valve is manually controlled to release the shield. This embodiment is also cumbersome in that it requires separate manual manipulation. It was therefore desirable to provide an improved valve which operated simply by the manipulation of relative trocar assembly housings during use of the trocar in a surgical procedure.